Cable terminal apparatus

ABSTRACT

A terminal apparatus for use with insulated power cable comprising a rigid housing having an elongated bore for receiving a terminal end portion of the cable, and an elastomeric sealing means at one end of the bore. The sealing means extends into the bore from said one end towards the opposite end for a distance substantially less than the length of the bore, and the remaining portion of the bore is filled with dielectric insulating fluid and a load bearing insulation system that maintains the sealing means in air-free sealing engagement between the bore and the cable regardless of service temperature variations.

United States Patent [32] Priority Jan. 26, 1968 [33] France [54] FLUID-TIGHT BUSHING FOR CRYOGENIC DEVICES 11 Claims, 2 Drawing Figs.

521 US. Cl 174/18 51 Im. Cl ..H01b 17/26. 50 Field of Search 174/s.c.,

FILLER [5 6] References Cited UNITED STATES PATENTS 1,868,410 7/1932 Dallenbach 174/12(.3)UX 1,905,751 4/1933 Rankin 174/12(.3)UX 3,059,044 10/ 1962 Friedrich et al 174/ 12(.3)X 3,440,326 4/1969 Lair 174/9 Primary Examiner- Laramie E. Askin Att0rney- Sughrue, Rothwell, Mion, Zinn and Macpeak ABSTRACT: An isothermal fluid-tight bushing for an .electric conductor leading between two spaces one of which is isothermal, consists of a substantially tubular member of ceramic material which, in conjunction with a wall to which the member is connected, defines the separation between the two spaces and two junction means respectively connecting the ceramic member with the conductor and the wall. Each junction means consists of a stainless steel element connected to the conductor or the wall, as the case may be, a bellows connected to the element and a junction member connected between the bellows and the ceramic member, W

Apnl 27, 1971 FQMOISSON-FRANCKHAUSER ET AL 3,

FLUID-TIGHT BUSHING FOR CRYOGENIC DEVICES Filed Jan.'17. 1969 2 Smite-Sheet I FIG.2

OVACUUM 7 TAINLESS STEEL a 'TEFLON" '1 FLUID-TIGHT BUSHING FOR CRYOGENIC DEVICES BACKGROUND OF THE INVENTION The present invention relates to an isothermal, insulating and fluid-tight, bushing between two enclosed spaces one of which is cryogenic, and its applications, more particularly, in cryo-connections as bushing equipment leading from a cryogenic enclosed space under pressure to an enclosed space in which a vacuum is present, for example for a cryogenic conductor carrying heavy currents at high voltage.

The invention relates more particularly to cryogenic conductors, i.e. to conductors operating at low temperature. These conductors, for example of the superconducting type, which are intended to carry electric current, consist of metal of a high degree of purity, the electrical resistivity of which is greatly reduced when they are brought to low temperature.

The invention is also applicable to conductors having superconducting properties when they are brought to a temperature below a given temperature, namely the critical temperature, below which superconductivity is set up.

Thus, a cryogenic connection comprises an electric conductor, a device for cooling the conductor by the circulation of cryogenic fluid, electric insulation between the electric conductor and the earthed parts, and thermal insulation for reducing to a minimum any heat transfer between the enclosed space containing the cooling fluid and the surrounding medium.

In such a connection, the electric conductor may consist of an aluminium conductor extending from a cryogenic enclosed space under pressure to another enclosed space in which a vacuum is present or which is under the pressure of conductor under voltage by any known electric insulating material. More particularly, the cryogenic enclosed spaces, being brought to earth potential, may consist of two tubes, for example of stainless steel, which are electrically insulated from the electric conductor. The wall separating the two enclosed spaces comprises, for example, ceramic material. One of the main difficulties encountered in constructing a cryo-connection results from the stresses which are exerted more particularly on the conductor and on the ceramic-metal junctions between the walls of the two enclosed cryogenic spaces when cooling is applied, and which are due to the differences of the expansions of the materials of which the cryo-connection is composed and to the pressure of the cryogenic fluid. These stresses may have the effect, in particular, of breaking the electric insulation between the two enclosed cryogenic spaces.

The present invention has for its object the provision of an isothermal fluid-tight bushing extending between a cryogenic space and a further space, which is resistent to stresses exerted on application of low temperature.

According to the present invention there is provided in combination with an electric conductor extending between two enclosed spaces one of which is cryogenic, an isothermal, insulating and fluid-tight, bushing including a member of ceramic material of substantially tubular form surrounding the conductor and first and second junction means respectively connecting the ceramic member to the electric conductor and to a wall defining with said ceramic member the separation between the two enclosed spaces, each said junction means comprising a stainless-steel element connected to the conductor or to the wall, as the case may be, and bearing on the ceramic member, a bellows connected to the stainless-steel element and a junction member connected between the bellows and the ceramic member.

In a particular embodiment, the stainless-steel element of the first junction means is a ring bearing on the ceramic menber.

:spectively connecting the ceramic member 6 to the conduc- In this particular embodiment, the bellows defines with i the stainless-steel element and annular space communicating with one of the enclosed spaces, being the space between the conductor and the ceramic member, through an aperture in the element, through which the annular space can be exhausted.

Preferably the electric conductor has a solid portion, for example of aluminium, in the space between the conductor and the ceramic member which space is exhausted and an enlarged portion comprising elemental conductors in the other space which is the cryogenic space, and resilient rings are disposed between the bushing and the enlarged portion of the conductor, so as to cause the bushing to be in compression. fatar'es and advantages of the invention will Further become apparent from the description given in the following with reference to the accompanying-drawings, in which:

FIG. 1 illustrates, by way of example, an axial sectional view of an isothermal bushing between a cryogenic enclosed space and an exhausted enclosed space relative to a cryoconnection comprising an electric conductor of the super- 7 conducting type; and

for example, gaseous helium at 20 K under a pressure of the order of 20 bars.

The enclosed cryogenic space 4 also surrounds the solid portion 1 of the electric conductor, so as to leave a space 5 between the said conductor 1 and a member 6 which, in conjunction with a wall 7, 18 to which the member 6 is secured, separates the cryogenic fluid and the vacuum. The space 5 communicates with an evacuated enclosed space 40 surrounding the enclosed cryogenic space 4, from which it is separated by the wall 7, and containing a thermal superinsulation of known type, by which the enclosed space 4 is thermally insulated from the surrounding ambient medium. The cryogenic enclosed space is connected to earth and for this purpose, and in order to avoid spark-over voltages in the cryogenic fluid, the member 6 opposite the solid conductor consists of ceramic material and is also given special dimensions which are readily determinable by the person skilled in the art. Likewise, the wall 7 consisting, for example, of stainless steel is protected by sheets 8 of electric insulating material, for example of polytetrafluoroethylene, perf erably wound on in a number of convolutions. In an alternative, sheets of the same material are disposed around the conductor in the inner enclosed space in the case where the latter contains a cryogenic fluid instead of being exhausted. First and second junction means are provided for retor 1 and to the wall 7 (through a wall part 18), the junction means together with the member 6 constituting a fluidtight isothermal bushing between the cryogenic fluid contained in the enclosed space 4 under helium at pressure and the interior of the evacuated space between the solid conductor 1 and the ceramic member.

The first junction means consists of a first ring 9 of stainless steel, preferably of small thickness, which is welded to the conductor 1, and of a second ring 10 of aluminium,

which partially surrounds the ring 9 and which is welded to of malleable metal, for example of indium, lead or tin. Resilient washers 17 known under the registered trade mark Schnorr are disposed between the head 2 and the ring 11, so as to cause the bushing to be in compression. A stainlesssteel bellows 13 is welded between the external ring 11 and a first metal flange 14a. preferably of stainless steel. the flange 1411 being welded to a tubular n'ng 14b soldered to the corresponding end of the ceramic member 6. The ring 14b is made of a material compatible with good soldering to the ceramic member 6, and will consist. for example, of a ferrous alloy such as the material known under the registered trade mark Kovar.

The ring 11 may be formed with an aperture 16 between the annular space defined by the bellows 13 and the evacuated space 5, thus placing under a vacuum the interior of the junction. Such an arrangement provides a fluid-tight bushing between an enclosed space containing gaseous helium under pressure and an exhausted space, for an electric conductor, intended more particularly for carrying heavy currents at high voltages, for example ofthe order of 10,000 A at 100 kV.

Similarly, for ensuring good fluid-tightness at the other end of the member 6, the junction means consists of a stainless-steel ring 19 connected between the wall 18 and the ceramic member 6. The ceramic member 6 rests on the ring 19 through a substantially annular seating 20, preferably of ma lsah m teltt re of indium- The ring 19 is secured to the ceramic member 6 by any known means. For example, if the material of which the metal wall consists lends itself thereto, the ring may be soldered to the wall; if soldering is not possible, a connection such as that illustrated in the figure may be made by means of screws such as 21. A packing such as that shown at 22 is then provided between the wall 18 and the member 19.

Fluid-tightness between the ring 19 and the second end of the member 6 is obtained by means of a metal bellows 23, of which one end is welded to the ring 19 and the other end is welded to a second metal ring 24, a tubular member 25 of material readily solderable to ceramic being soldered to the sec-. ond end of the ceramic member 6 and welded to the ring 24.

The ring 19 is formed with an aperture 27 affording communication between the annular space 28, defined by the members 19 and 24 and the bellows 23, and the exhausted space 5.

In- FIG. 2, which is an axial section through a cryoconnection of the same type as that of FIG. 1, the same reference numerals are used to denote like parts. This embodiment differs from the preceding one in the following respects: at the first end of the ceramic member 6, the ring 11 and the flange 14a are replaced by a single ring 31, for example of stainless steel, the bellows l3 consistingof a metal sealing diaphragm 33, to which the flange 14b is directly welded.

In addition, the junction of the second end of the member 6 is made by means of a stainless-steel flange 35 welded to the metal wall 7 and in contact with the end of the ceramic member 6 through a seating 36 of malleable metal, for example of indium, lead or tin.

Fluid-tightness is afforded by a metal bellows 37, preferably of stainless-steel, which is welded on the one hand to the flange 35 and on the other hand to a ring 39 soldered 'to the second end of the member 6, the ring 39 being made of a material compatible with good soldering to a ceramic material, for example .of the material known under the e ist d s m rk Kw When the electric conductor and the bushing between the cryogenic field and the vacuum are cooled to low temperature, the bushing affords great resistance to the stresses qsy l rssuhsrs nans ens res?! gsdfl i zti h t ss between the cryogenic space and the exhausted space, even when high currents and high voltages flow through electric conductor.

The isothermal fluid-tight bushing described in the foregoing between gaseous helium at K and a vacuum has been referred to by way of example and does not in any way limit the present invention. Indeed, the cryogenic fluid may be chosen from any cooling fluids, for example liquid helium, gaseous nitrogen, liquid or gaseous hydrogen, etc.,

and similarly the electric conductor may consist of any other material which is a good conductor of electricity, of hyperconducting or superconducting type. Likewise, the two enclosed spaces may contain cryogenic fluids of like nature or of different natures, under equal or different pressures.

iwh atjwe claim is:

1. In combination with an electric conductor extending between two enclosed spaces, one of which is cryogenic, an isothermal, insulating and fluid-tight bushing including a member of ceramic material of substantially tubular form surrounding the conductor and first and second junction means respectively connecting the ceramic member to the electric conductor and to a wall defining with said ceramic member the separation between the two enclosed spaces, each said junction means comprising a stainless'steel element connected to the conductor or to the wall, as the case may be, and bearing on the ceramic member, a bellows con nected to the stainless-steel element and a junction member connected between the bellows and the ceramic member, said bellows of said first junction means defining with said element an annular space communicating with one of the enclosed spaces and being the space between the ceramic member and the conductor, and an aperture in said element through which said annular space can be exhausted.

2. The bushing as claimed in claim 1, wherein the stain less-steel element of the first junction means comprises a ring and a flange coaxial therewith.

3. In combination with an electric conductor extending between two enclosed spaces, one of which is cryogenic, an isothermal, insulating and fluid-tight bushing including a member of ceramic material of substantially tubular form surrounding the conductor and first and second junction means respectively connecting the ceramic member to the electric conductor and to a wall defining with said ceramic member, the separation between two enclosed spaces,

each said junction means comprising a stainless-steel element connected to the conductor or to the wall, as the case may be, and bearing on the ceramic member, a bellows connected to the stainless-steel element, a junction ififinefeaiihateaveen the bellows and the ceramic member, said stainless steel element of said second junction means comprising a first ring secured to the ceramic member and, in a fluid-tight manner, to "said wall, and a second ring secured on the one hand to the associated junction member and on the other hand to the associated bellows.

4. The bushing as claimed in claim 3, wherein the stainless-steel element of the second junction means defines with the associated bellows an annular space and said stainless steel element carries an aperture for communicating said annular space with the space between the conductor and .the ceramic member, allowing said annular space to be exhausted. 5. An insulative and fluid-tight bushing for passing an electrical conductor into a cryogenic enclosure through an opening in the cryogenic wall thereof comprising:

a ceramic sleeve located inside the opening, coaxial with and spaced from the conductor and the cryogenic enclosure wall;

a first stainless-steel ring sealed to the cryogenic ena 6 A bu shin g as claimed in claim 3, further including means,

for connecting the space between the sleeve and the conductor with a vacuum chamber containing the conductor and surrounding the cryogenic enclosure.

10. A bushing as claimed in claim 5; further inc ludinga cylindrical flange on the conductor provided on the side of the second stainless-steel ring facing the cryogenic enclosure, and a spring is located between the second ring and the flange to compress the bushing by urging the second steel ring toward the first.

11. A bushing as claimed in claim 5, in which the first steel ring is also sealed to the first end of the sleeve. 

1. A terminal apparatus for insulated power cable comprising an elongated housing receiving a terminal end portion of said cable deformable sealing means closing one end of said housing around said cable in an air-free seal, a conducting terminal adjacent an opposite end of said housing connected to said power cable, thrust means exerting end thrust on said sealing means and maintaining the same in air-free sealing engAgement between said housing and said cable, thrust bearing dielectric means in said housing between said terminal and said sealing means, and dielectric fluid in said housing between said sealing means and said terminal.
 2. The terminal apparatus of claim 1 wherein said sealing means includes a tubular elastomeric filler mounted on said cable, said filler being substantially shorted in axial length than the distance between said filler and said terminal.
 3. The terminal apparatus of claim 2 wherein said thrust bearing dielectric means includes at least one annular ring mounted on said cable and having an end face transmitting compressive force against an end face of said filler.
 4. The terminal apparatus of claim 3 including a plurality of said annular rings in end-to-end relation, one of said rings having a conically tapered end surface adjacent the end of an adjacent ring and passage means in one of said rings for permitting the flow of dielectric fluid between the inside and outside of said rings.
 5. The terminal apparatus of claim 1 wherein said thrust means includes at least one compression springs.
 6. The terminal apparatus of claim 5 wherein said thrust means includes means for adjusting the compression on said spring to control the thrust exerted on said sealing means.
 7. The terminal apparatus of claim 6 including visual marker means operatively associated with said thrust means for indicating when a desired compression of said spring is obtained with said adjusting means.
 8. A terminal apparatus for power cable of the type including a central conductor and surrounding insulation, said apparatus comprising a housing having an elongated bore for receiving an end portion of said cable, an elastomeric sealing means projecting into said bore for a distance substantially less than the length of said bore, dielectric fluid in said bore above said sealing means, and thrust bearing insulator means maintaining said seal means in sealing engagement between the bore and said cable.
 9. The terminal apparatus of claim 8 including thrust means comprising at least one compression spring exerting force on said insulator means and maintaining sealing engagement of said sealing means.
 10. The terminal apparatus of claim 9 including means operatively associated with said spring for adjusting the compression of said spring.
 11. The terminal apparatus of claim 8 including terminal means mounted adjacent an opposite end of said housing and connected to the central conductor of said cable.
 12. The terminal apparatus of claim 8 including thrust means comprising a ring member supported from said housing and at least one compression spring disposed between said ring member and an end face of said insulator means.
 13. The terminal apparatus of claim 12 wherein said ring member extends around said cable and said spring is in coaxial alignment around said cable.
 14. A terminal apparatus for insulated power cable comprising an elongated housing assembly receiving a terminal end portion of said cable, annular deformable sealing means within said housing assembly around said cable, thrust means applying axial thrust to said sealing means and maintaining said sealing means in sealing engagement between said housing assembly and said cable, and dielectric fluid within said housing assembly above said sealing means.
 15. The terminal apparatus of claim 14 wherein said sealing means includes a tubular elastomeric filler mounted on the insulation of said cable, said filler being substantially shorter in axial length than the end portion of said cable.
 16. A terminal apparatus for insulated power cable comprising an elongated housing assembly receiving a terminal end portion of said cable, annular deformable sealing means within said housing assembly around said cable, thrust means including at least one annular insulating ring mounted on said cable transmitting compressive force on said sealing means and maintaining said sealing means in sealing engagement bEtween said housing assembly and said cable, and dielectric fluid within said housing assembly above said sealing means.
 17. The terminal apparatus of claim 16 wherein said thrust means includes at least one compression spring.
 18. The terminal apparatus of claim 17 wherein said thrust means include s means for adjusting the compression on said spring to control the thrust exerted on said sealing means.
 19. The terminal apparatus of claim 17 including visual marker means operatively associated with said thrust means for indicating when a desired compression of said spring is obtained with said adjusting means.
 20. The terminal apparatus of claim 16 including a plurality of said annular rings in end-to-end relation, one of said rings having a conically tapered end surface adjacent the end of an adjacent ring and passage means in one of said rings for permitting the flow of dielectric fluid between the inside and outside of said rings. 